Preparation of the serum phosphorus fractions of catfish,pelteobagrus vachelli,including protein linked phosphorus(PLP),lipid soluble phosphorus(LP),inorganic phosphorus(IP) were carried out by the methods of organic solvent extraction and the three phosphorus fractions in the same sample as well as total serum phosphorus were determined by the methods of (NH 4) 2MoO 4 SnCl 2 and (NH 4) 2MoO 4 Vc reduction respectively.The ranges of recovery rates in two above methods were 97.1%～98.3%,95.2%～97.5% respectively.The serum phosphorus of 148 female catfish and 111 male catfish were determined by the way.The results showed that serum protein linked phosphorus content was a reliable indicator of sex determination and ovarian development.The serum phosphorus fractions fluctuated with ovarian development of the catfish.
